Heat removal and recovery in biomass pyrolysis

ABSTRACT

Pyrolysis methods and apparatuses that allow effective heat removal, for example when necessary to achieve a desired throughput or process a desired type of biomass, are disclosed. According to representative methods, the use of a quench medium (e.g., water), either as a primary or a secondary type of heat removal, allows greater control of process temperatures, particularly in the reheater where char, as a solid byproduct of pyrolysis, is combusted. Quench medium may be distributed to one or more locations within the reheater vessel, such as above and/or within a dense phase bed of fluidized particles of a solid heat carrier (e.g., sand) to better control heat removal.

FIELD OF THE INVENTION

The present invention relates to pyrolysis methods and apparatuses inwhich a solid heat carrier (e.g., sand) is separated from the pyrolysisreactor effluent and cooled with a quench medium (e.g., water) toimprove temperature control. Cooling with quench medium may occur in orabove a fluidized bed of the heat carrier, in which solid char byproductis combusted to provide some or all of the heat needed to drive thepyrolysis.

DESCRIPTION OF RELATED ART

Environmental concerns over fossil fuel greenhouse gas emissions haveled to an increasing emphasis on renewable energy sources. Wood andother forms of biomass including agricultural and forestry residues areexamples of some of the main types of renewable feedstocks beingconsidered for the production of liquid fuels. Energy from biomass basedon energy crops such as short rotation forestry, for example, cancontribute significantly towards the objectives of the Kyoto Agreementin reducing greenhouse gas (GHG) emissions.

Pyrolysis is considered a promising route for obtaining liquid fuels,including transportation fuel and heating oil, from biomass feedstocks.Pyrolysis refers to thermal decomposition in the substantial absence ofoxygen (or in the presence of significantly less oxygen than requiredfor complete combustion). Initial attempts to obtain useful oils frombiomass pyrolysis yielded predominantly an equilibrium product slate(i.e., the products of “slow pyrolysis”). In addition to the desiredliquid product, roughly equal proportions of non-reactive solids (charand ash) and non-condensible gases were obtained as unwanted byproducts.More recently, however, significantly improved yields of primary,non-equilibrium liquids and gases (including valuable chemicals,chemical intermediates, petrochemicals, and fuels) have been obtainedfrom carbonaceous feedstocks through fast (rapid or flash) pyrolysis atthe expense of undesirable, slow pyrolysis products.

Fast pyrolysis refers generally to technologies involving rapid heattransfer to the biomass feedstock, which is maintained at a relativelyhigh temperature for a very short time. The temperature of the primarypyrolysis products is then rapidly reduced before chemical equilibriumis achieved. The fast cooling therefore prevents the valuable reactionintermediates, formed by depolymerization and fragmentation of thebiomass building blocks, namely cellulose, hemicellulose, and lignin,from degrading to non-reactive, low-value final products. A number offast pyrolysis processes are described in U.S. Pat. No. 5,961,786;Canadian Patent Application 536,549; and by Bridgwater, A.V., “BiomassFast Pyrolysis,” Review paper BIBLID: 0354-9836, 8 (2004), 2, 21-49.Fast pyrolysis processes include Rapid Thermal Processing (RTP), inwhich an inert or catalytic solid particulate is used to carry andtransfer heat to the feedstock. RTP has been commercialized and operatedwith very favorable yields (55-80% by weight, depending on the biomassfeedstock) of raw pyrolysis oil.

Pyrolysis processes such as RTP therefore rely on rapid heat transferfrom the solid heat carrier, generally in particulate form, to thepyrolysis reactor. The combustion of char, a solid byproduct ofpyrolysis, represents an important source of the significant heatrequirement for driving the pyrolysis reaction. Effective heatintegration between, and recovery from, the pyrolysis reaction andcombustion (or reheater) sections represents a significant objective interms of improving the overall economics of pyrolysis, under theoperating constraints and capacity of the equipment, for a givenfeedstock. As a result, there is an ongoing need in the art forpyrolysis methods with added flexibility in terms of managing thesubstantial heat of combustion, its transfer to the pyrolysis reactionmixture, and its recovery for use in other applications.

SUMMARY OF THE INVENTION

The present invention is associated with the discovery of pyrolysismethods and apparatuses that allow effective heat removal, for examplewhen necessary to achieve a desired throughput. Depending on thepyrolysis feed used, the processing capacity may become constrained, notby the size of the equipment, but by the ability to remove heat from theoverall system, as required to operate within design temperatures. Whilesome heat removal schemes, such as passing the recycled heat carrier(e.g., sand) through a cooler, may be effective in certaincircumstances, they may not be applicable to all pyrolysis systems interms of meeting cost and performance objectives. The methods andapparatuses described herein, involving the use of a quench medium,represent generally less expensive alternatives for providing neededheat removal. The quench medium may be used effectively alone or incombination with other types of cooling, for example a sand cooler.

The quench medium may therefore act as either a primary or secondarytype of heat removal, allowing greater control of process temperatures,and particularly in the reheater where char, as a solid byproduct ofpyrolysis, is combusted. Associated with this heat removal is addedoperational flexibility in terms of biomass feedstock type andprocessing capacity, which are often constrained by a maximum operatingtemperature rather than equipment size. In a particular of pyrolysisoperation, a quench medium is distributed to one or more locationswithin the reheater vessel, thereby cooling this vessel if a sand cooleris either not used (e.g., in view of cost considerations) or otherwiseremoves excess heat to an insufficient extent. Often, the reheatervessel is operated with a fluidized bed of particles of the solid heatcarrier, through which an oxygen-containing combustion medium is passed,in order to combust the char and generate some or all of the heatrequired for the pyrolysis. The fluidized bed comprises a dense phasebed below a dilute phase of the particles of the solid heat carrier.

A quench medium may be sprayed, for example, on the top of a heatcarrier such as sand, residing in the reheater as a fluidized particlebed. Heat is thereby removed, for example, by conversion of water, as aquench medium, to steam. The consumption of heat advantageously reducesthe overall temperature of the reheater and/or allows the pyrolysis unitto operate at a target capacity. Distributors may be located in variouspositions to introduce the quench medium at multiple points, for examplewithin the dense phase bed and/or in the dilute phase, above the densephase. Dilute phase introduction of the quench medium helps preventdense phase bed disruptions due to sudden volume expansion (e.g., ofwater upon being converted to steam) in the presence of a relativelyhigh density of solid particles. Such disruptions may detrimentally leadto increased solid particle entrainment and losses. Dense phaseintroduction (e.g., directly into a middle section of the dense phasebed), on the other hand, provides direct cooling of the solid particles.Such cooling is effective if introduction is carried out with sufficientcontrol, and at a quench medium flow rate, that avoids significantdisruptions of the dense phase bed. In some cases, quench medium may beintroduced both into, and above, the dense phase bed, and even atmultiple locations within and above the bed.

Embodiments of the invention are therefore directed to pyrolysis methodscomprising combining biomass and a solid heat carrier (e.g., solidparticulate that has been heated in a reheater and recycled) to providea pyrolysis reaction mixture, for example in a Rapid Thermal Processing(RTP) pyrolysis unit. The reaction mixture may, for example, be formedupon mixing the biomass and solid heat carrier at the bottom of, orbelow, an upflow pyrolysis reactor. The mixture is then subjected topyrolysis conditions, including a rapid increase in the temperature ofthe biomass to a pyrolysis temperature and a relatively short residencetime at this temperature, to provide a pyrolysis effluent. Theappropriate conditions are normally achieved using an oxygen-depleted(or oxygen-free) transport gas that lifts the pyrolysis reaction mixturethrough an upflow pyrolysis reactor. Following pyrolysis, the pyrolysiseffluent is separated (e.g., using a cyclone separator) into (1) asolids-enriched fraction comprising both solid char and a recycledportion of the solid heat carrier and (2) a solids-depleted fractioncomprising pyrolysis products. Pyrolysis products include, followingcooling, (1) liquid pyrolysis products that are condensed, such as rawpyrolysis oil and valuable chemicals, as well as (2) non-condensablegases such as H₂, CO, CO₂, methane, and ethane. The solids-enrichedfraction is then contacted with an oxygen-containing combustion medium(e.g., air or nitrogen-enriched air) to combust at least a portion ofthe solid char and reheat the recycled portion of the heat carrier,which in turn transfers heat to the pyrolysis reaction mixture. Asdiscussed above, the solids-enriched fraction is also contacted, forexample in a reheater containing a fluidized bed of the heat carrier,with a quench medium to reduce or limit the temperature in the reheateror otherwise the temperature of the recycled portion of the solid heatcarrier.

Further embodiments of the invention are directed to apparatuses forpyrolysis of a biomass feedstock. Representative apparatuses comprise anupflow, entrained bed pyrolysis reactor that may include, for example, atubular reaction zone. The apparatuses also comprise a cyclone separatorhaving (1) an inlet in communication with an upper section (e.g., apyrolysis effluent outlet) of the reactor (2) a solids-enriched fractionoutlet in communication with a reheater, and (3) a solids-depletedfraction outlet in communication with a pyrolysis product condensationsection. The apparatuses further comprise a quench liquid distributionsystem in communication with the reheater, for the introduction ofquench medium and consequently the removal of heat from within thisvessel.

Yet further embodiments of the invention are directed to a reheater forcombusting solid char that is separated from a pyrolysis effluent.Combustion occurs in the presence of a solid heat carrier that isrecycled to the pyrolysis reactor. The reheater comprises one or morepoints of quench medium introduction. In the case of multiple points ofintroduction, these will generally be positioned at different axiallengths along the reheater. Points of introduction may also includedistributors of the quench medium, as well as control systems forregulating the flow of the quench medium, for example, in response to ameasured temperature either in the dense phase bed or dilute phase ofthe solid heat carrier.

These and other embodiments and aspects relating to the presentinvention are apparent from the following Detailed Description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a representative pyrolysis process including a reactorand reheater.

FIG. 2 is a close-up view of quench medium entering a reheater bothwithin a dense phase bed of solid heat carrier, as well as in a dilutephase above the dense phase bed.

The features referred to in FIGS. 1 and 2 are not necessarily drawn toscale and should be understood to present an illustration of theinvention and/or principles involved. Some features depicted have beenenlarged or distorted relative to others, in order to facilitateexplanation and understanding. Pyrolysis methods and apparatuses, asdescribed herein, will have configurations, components, and operatingparameters determined, in part, by the intended application and also theenvironment in which they are used.

DETAILED DESCRIPTION

According to representative embodiments of the invention, the biomasssubjected to pyrolysis in an oxygen depleted environment, for exampleusing Rapid Thermal Processing (RTP), can be any plant material, ormixture of plant materials, including a hardwood (e.g., whitewood), asoftwood, or a hardwood or softwood bark. Energy crops, or otherwiseagricultural residues (e.g., logging residues) or other types of plantwastes or plant-derived wastes, may also be used as plant materials.Specific exemplary plant materials include corn fiber, corn stover, andsugar cane bagasse, in addition to “on-purpose” energy crops such asswitchgrass, miscanthus, and algae. Short rotation forestry products, asenergy crops, include alder, ash, southern beech, birch, eucalyptus,poplar, willow, paper mulberry, Australian blackwood, sycamore, andvarieties of paulownia elongate. Other examples of suitable biomassinclude organic waste materials, such as waste paper and construction,demolition, and municipal wastes.

A representative pyrolysis method is illustrated in FIG. 1. According tothis embodiment, biomass 10 is combined with solid heat carrier 12,which has been heated in reheater 100 and recycled. Biomass 10 isgenerally subjected to one or more pretreatment steps (not shown),including particle size adjustment and drying, prior to being combinedwith solid heat carrier 12. Representative average particle sizes forbiomass 10 are typically from about 1 mm to about 10 mm. Upon beingcombined with solid heat carrier 12, biomass 10 becomes rapidly heated,for example in a mixing zone 14 located at or near a lower section(e.g., the bottom) of pyrolysis reactor 200 that contains an elongated(e.g., tubular) reaction zone 16. The relative quantity of solid heatcarrier 12 may be adjusted as needed to achieve a desired rate oftemperature increase of biomass 10. For example, weight ratios of thesolid carrier 12 to biomass 10 from about 10:1 to about 500:1 arenormally used to achieve a temperature increase of 1000° C./sec (1800°F./sec) or more.

The combination of biomass 10 and solid heat carrier 12 therefore formsa hot pyrolysis reaction mixture, having a temperature generally fromabout 300° C. (572° F.) to about 1100° C. (2012° F.), and often fromabout 400° C. (752° F.) to about 700° C. (1292° F.). The temperature ofthe pyrolysis reaction mixture is maintained over its relatively shortduration in reaction zone 16, prior to the pyrolysis effluent 24 beingseparated. A typical pyrolysis reactor operates with the flow of thepyrolysis reaction mixture in the upward direction (e.g., in an upflow,entrained bed pyrolysis reactor), through reaction zone 16, such thatpyrolysis conditions are maintained in this zone for the conversion ofbiomass 10. Upward flow is achieved using transport gas 13 containinglittle or no oxygen, for example containing some or all ofnon-condensable gases 18 obtained after condensing liquid pyrolysisproduct(s) 20 from a solids-depleted fraction 22, comprising a mixtureof gaseous and liquid pyrolysis products. These non-condensable gases 18normally contain H₂, CO, CO₂, methane, and/or ethane. Some oxygen mayenter the pyrolysis reaction mixture, however, from reheater 100, wherechar is combusted in the presence of oxygen-containing combustion medium28, as discussed in greater detail below.

Transport gas 13 is therefore fed to pyrolysis reactor 200 at a flowrate sufficient to attain a gas superficial velocity through mixing zone14 and reaction zone 16 that entrains the majority, and usuallysubstantially all, solid components of the pyrolysis reaction mixture.Representative gas superficial velocities are greater than 1 meter persecond, and often greater than 2 meters per second. The transport gas 13is shown in FIG. 1 entering a lower section of mixing zone 14 of reactor200. The superficial velocity of this gas in reaction zone 16 is alsosufficient to obtain a short residence time of the pyrolysis reactionmixture in this zone, typically less than about 2 seconds. As discussedabove, rapid heating and a short duration at the reaction temperatureprevent formation of the less desirable equilibrium products in favor ofthe more desirable non-equilibrium products. Solid heat carriers,suitable for transferring substantial quantities of heat for rapidheating of biomass 10 include inorganic particulate materials having anaverage particle size typically from about 25 microns to about 1 mmRepresentative solid heat carriers are therefore inorganic refractorymetal oxides such as alumina, silica, and mixtures thereof. Sand is apreferred solid heat carrier.

The pyrolysis reaction mixture is subjected to pyrolysis conditions,including a temperature, and a residence time at which the temperatureis maintained, as discussed above. Pyrolysis effluent 24 comprising thesolid pyrolysis byproduct char, the solid heat carrier, and thepyrolysis products, is removed from an upper section of pyrolysisreactor 200, such as the top of reaction zone 16 (e.g., a tubularreaction zone) of this reactor 200. Pyrolysis products, comprising bothnon-condensable and condensable components of pyrolysis effluent 24, maybe recovered after separation of solids, including char and heatcarrier. Cooling, to promote condensation, and possibly furtherseparation steps are used to provide one or more liquid pyrolysisproduct(s). A particular liquid pyrolysis product of interest is rawpyrolysis oil, which generally contains 30-35% by weight of oxygen inthe form of organic oxygenates such as hydroxyaldehydes, hydroxyketones,sugars, carboxylic acids, and phenolic oligomers as well as dissolvedwater. For this reason, although a pourable and transportable liquidfuel, the raw pyrolysis oil has only about 55-60% of the energy contentof crude oil-based fuel oils. Representative values of the energycontent are in the range from about 19.0 MJ/liter (69,800 BTU/gal) toabout 25.0 MJ/liter (91,800 BTU/gal). Moreover, this raw product isoften corrosive and exhibits chemical instability due to the presence ofhighly unsaturated compounds such as olefins (including diolefins) andalkenylaromatics.

Hydroprocessing of this pyrolysis oil is therefore beneficial in termsof reducing its oxygen content and increasing its stability, therebyrendering the hydroprocessed product more suitable for blending infuels, such as gasoline, meeting all applicable specifications.Hydroprocessing involves contacting the pyrolysis oil with hydrogen andin the presence of a suitable catalyst, generally under conditionssufficient to convert a large proportion of the organic oxygen in theraw pyrolysis oil to CO, CO₂ and water that are easily removed. The term“pyrolysis oil,” as it applies to a feedstock to the hydroprocessingstep, refers to the raw pyrolysis oil obtained directly from pyrolysis(e.g., RTP) or otherwise refers to this raw pyrolysis oil after havingundergone pretreatment such as filtration to remove solids and/or ionexchange to remove soluble metals, prior to the hydroprocessing step.

As illustrated in the embodiment of FIG. 1, pyrolysis effluent 24,exiting the upper section of pyrolysis reactor 200, is separated usingcyclone 300 into solids-enriched and solids-depleted fractions 26, 22.These fractions are enriched and depleted, respectively, in their solidscontent, for example measured in weight percent, relative to pyrolysiseffluent 24. Solids-enriched fraction 26 comprises a substantialproportion (e.g., greater than about 90% by weight) of the solid charand solid heat carrier contained in pyrolysis effluent 24. In additionto char, solids-enriched fraction also generally contains other lowvalue byproducts of pyrolysis, such as coke and heavy tars. According toalternative embodiments, multiple stages of solids separation (e.g.,using two or more cyclones) may be used to improve separationefficiency, thereby generating multiple solids-enriched fractions, someor all of which enter reheater 100. In any event, the portion of solidheat carrier contained in pyrolysis effluent and entering reheater 100,whether in one or more solids-enriched fractions, is namely a recycledportion. This recycled portion, in addition to the solid char exitingcyclone 300 and possibly other solids separators, enter reheater 100used to combust the char and reheat the solid heat carrier for furtheruse in transferring heat to biomass 10.

Solids-depleted fraction 22 may be cooled, for example using cooler 400to condense liquid pyrolysis products such as raw pyrolysis oil andoptionally, following additional separation/purification steps, valuablechemicals including carboxylic acids, phenolics, and ketones. Asillustrated in FIG. 1, cooled pyrolysis product 42 is passed toseparator 500 which may be a single-stage flash separator to separatenon-condensable gases 18 from liquid pyrolysis product(s) 20. Otherwise,multiple stages of vapor-liquid equilibrium contacting may be achievedusing suitable contacting devices such as contacting trays or solidpacking materials.

Rapid cooling of solids-depleted fraction 22 is generally desired tolimit the extent of pyrolysis reactions occurring beyond the relativelyshort residence time in reaction zone 16. Cooling may be achieved usingdirect or indirect heat exchange, or both types of heat exchange incombination. An example of a combination of heat exchange types involvesthe use of a quench tower in which a condensed liquid pyrolysis productis cooled indirectly, recycled to the top of the tower, and contactedcounter-currently with the hot, rising vapor of solids-depleted fraction22. As discussed above, solids-depleted fraction 22 comprises gaseousand liquid pyrolysis products, including raw pyrolysis oil that isrecovered in downstream processing. Accordingly, cyclone 300 has (i) aninlet in communication with an upper section of pyrolysis reactor 200,in addition to (ii) a solids-enriched fraction outlet in communicationwith reheater 100 and (iii) a solids-depleted fraction outlet incommunication with a pyrolysis product condensation section. Namely, thecyclone inlet may correspond to the conduit for pyrolysis effluent 24,the solids-enriched fraction outlet may correspond to the conduit forsolids-enriched fraction 26, and the solids-depleted fraction outlet maycorrespond to the conduit for solids-depleted fraction 22. Arepresentative pyrolysis product condensation section may correspond tocooler 400 and separator 500.

As illustrated in the representative embodiment of FIG. 1,solids-enriched fraction 26 exiting cyclone 300 (possibly in combinationwith one or more additional solids-enriched fractions) is contacted withan oxygen-containing combustion medium 28 in reheater 100 to combust atleast a portion of the solid char entering this vessel withsolids-enriched fraction 26. A representative oxygen-containingcombustion medium is air. Nitrogen-enriched air may be used to limit theadiabatic temperature rise of the combustion, if desired. The combustionheat effectively reheats the recycled portion of the solid carrier. Theheated solid carrier is, in turn, used for the continuous transfer ofheat to the pyrolysis reaction mixture, in order to drive the pyrolysisreaction. As discussed above, reheater 100 generally operates as afluidized bed of solid particles, with the oxygen-containing combustionmedium serving as a fluidization medium, in a manner similar inoperation to a catalyst regenerator of a fluid catalytic cracking (FCC)process, used in crude oil refining. Combustion generates flue gas 32exiting reheater 100, and, according to some embodiments, flue gas 32may be passed to a solids separator such as cyclone 300 to removeentrained solids. The fluidized bed comprises dense phase bed 30 (e.g.,a bubbless, bubbling, slugging, turbulent, or fast fluidized bed) of thesolid heat carrier in a lower section of reheater 100, below a dilutephase 40 of these particles, in an upper section of reheater 100. One ormore cyclones may also be internal to reheater 100, for performing thedesired separation of entrained solid particles and return to densephase bed 30.

Aspects of the invention relate to the use of a quench medium forimproving the overall management of heat in pyrolysis systems. Forexample, heat removal from the solid carrier, and heat transfer to thequench medium, may be achieved by direct heat exchange between thequench medium and the solid carrier. Advantageously, the temperature ofthe recycled portion of the solid heat carrier, which is passed toreheater 100 as described above, is limited (e.g., to a maximum designtemperature) by direct contact between this solid heat carrier andquench medium 44 in reheater 100. In some cases, this limitation of thecombustion temperature can allow an increase in the operating capacityof the overall pyrolysis system. A preferred quench medium is water oran aqueous solution having a pH that may be suited to the constructionmaterial of the reheater or otherwise may have the capability toneutralize rising combustion gases. In some cases, for example, the useof dilute caustic solution, having in pH in the range from about 8 toabout 12, can effectively neutralize acidic components present in thecombustion gases. Preferably, quench medium 44 is introduced to reheater100 through distributor 46.

FIG. 2 illustrates, in greater detail, a particular embodiment ofcontacting the quench medium with the solids-enriched fraction recoveredfrom the pyrolysis effluent. According to this embodiment, a quenchliquid distribution and control system is in communication with thereheater. In particular, FIG. 2 shows portions of quench medium 44 a, 44b being introduced to reheater 100 at two separate points (to whichconduits for quench medium portions 44 a, 44 b lead) along its axiallength. In general, therefore, the quench medium may be introduced atone or more positions along the axial length of the reheater and/or atone or more radial positions at a given axial length. Also, the quenchmedium may be introduced through one or more distributors at the one ormore positions of introduction. According to the embodiment depicted inFIG. 2, a portion of quench medium 44 b is introduced to reheater 100above dense phase bed 30 of solid particulate comprising a recycledportion of the solid heat carrier, as described above. This portion ofthe quench medium is directed downwardly toward the surface of densephase bed 30, but disruption of the bed is relatively minor, asvaporization of the quench medium occurs primarily in dilute phase 40.Also shown in FIG. 2 is another portion of quench medium 44 a,introduced within dense phase bed 30 of the solid heat carrier, throughdistributor 46. Disruption of dense phase bed 30 is increased, butdirect heat transfer is also increased, relative to the case ofintroduction of the portion of quench medium 44 b into dilute phase 40.Introduction of quench medium into both dense phase bed 30 and dilutephase 40, for example at differing rates and/or at differing times,therefore allows alternative types of control (e.g., coarse control andfine control, respectively) of heat removal. According to furtherembodiments, the methods described herein may further comprise flowingat least a portion of the solid heat carrier through a heat exchanger(not shown) such as a sand cooler, thereby adding another type of heatremoval control.

According to the quench liquid distribution and control system depictedin the particular embodiment of FIG. 2, flows of portions of the quenchmedium 44 a, 44 b, introduced within and above dense phase bed 30, arecontrolled in response to temperatures measured within and above densephase bed 30, respectively. Therefore, temperature elements TE in densephase bed 30 and dilute phase 40, communicate through temperaturetransmitters TT and temperature indicator controllers TIC to temperaturecontrol valves TV. These valves, in response to the measuredtemperatures, adjust their variable percentage openings, as needed toprovide sufficient flows of portions of quench medium 44 a, 44 b, inorder to control the temperatures measured at temperature elements TE.Therefore, in response to a measured temperature in reheater 100 that isbeyond a set point temperature, for example, due to an increase in flowrate, or a change in type, of biomass 10, the appropriate TIC(s) sendsignal(s) to the corresponding temperature control valve(s), whichrespond by increasing quench medium flow rate to reheater 100,optionally through one or more distributors 46. Accordingly, the quenchliquid distribution and control systems described herein can effectivelyprovide the greater operational flexibility needed in pyrolysisoperations, in which increased capacity and/or the processing ofvariable biomass types is desired. A particular quench liquiddistribution and control system is therefore represented by thecombination of TE, TT, TIC, and TV, controlling the quench mediumintroduction at a given point.

Overall, aspects of the invention are directed to pyrolysis methods withimproved heat control, and especially reheaters for combusting solidchar, separated from a pyrolysis effluent, in the presence of a solidheat carrier that is recycled to the pyrolysis reactor to transfer heatand drive the pyrolysis. Advantageously, the reheater comprises one ormore points of quench medium introduction along its axial length,optionally together with quench medium distributors and control systemsas described above. Those having skill in the art, with the knowledgegained from the present disclosure, will recognize that various changescould be made in these pyrolysis methods without departing from thescope of the present invention. Mechanisms used to explain theoreticalor observed phenomena or results, shall be interpreted as illustrativeonly and not limiting in any way the scope of the appended claims.

1. A pyrolysis method comprising: (a) combining biomass and a solid heatcarrier to provide a pyrolysis reaction mixture; (b) subjecting thepyrolysis reaction mixture to pyrolysis conditions to provide apyrolysis effluent; (c) separating, from the pyrolysis effluent, (1) asolids-enriched fraction comprising solid char and a recycled portion ofthe solid heat carrier and (2) a solids-depleted fraction comprisinggaseous and liquid pyrolysis products; (d) contacting thesolids-enriched fraction with (1) an oxygen-containing combustion mediumto combust at least a portion of the solid char and reheat the recycledportion of the solid heat carrier and (2) a quench medium to limit thetemperature of the recycled portion of the solid heat carrier.
 2. Thepyrolysis method of claim 1, wherein the biomass selected from the groupconsisting of hardwood, softwood, hardwood bark, softwood bark, cornfiber, corn stover, sugar cane bagasse, switchgrass, miscanthus, algae,waste paper, construction waste, demolition waste, municipal waste, andmixtures thereof.
 3. The pyrolysis method of claim 1, wherein thepyrolysis conditions include a temperature from about 400° C. (752° F.)to about 700° C. (1292° F.) and a pyrolysis reactor residence time ofless than about 2 seconds.
 4. The method of claim 1, wherein, in step(a), the biomass and the heat carrier are combined below a pyrolysisreaction zone.
 5. The method of claim 4, wherein the pyrolysis reactionzone is within an upflow, entrained bed reactor.
 6. The method of claim1, wherein the quench medium comprises water.
 7. The method of claim 1,wherein the oxygen-containing combustion medium comprises air.
 8. Themethod of claim 1, wherein the contacting in step (d) is carried out ina reheater containing a fluidized bed of the solid heat carrier.
 9. Themethod of claim 8, wherein the quench medium is introduced to thereheater at one or more positions along its axial length.
 10. The methodof claim 9, wherein the quench medium is introduced to the reheaterthrough one or more distributors at the one or more positions at whichquench medium is introduced.
 11. The method of claim 8, wherein thequench medium is introduced to the reheater above a dense phase bed ofthe heat carrier.
 12. The method of claim 11, wherein flow of the quenchmedium, introduced to the reheater above the dense phase bed, iscontrolled in response to a temperature measured above the dense phasebed.
 13. The method of claim 11, wherein the quench medium is directeddownwardly toward the surface of the dense phase bed.
 14. The method ofclaim 8, wherein the quench medium is introduced to the reheater withina dense phase bed of the heat carrier.
 15. The method of claim 14,wherein flow of the quench medium, introduced to the reheater within thedense phase bed, is controlled in response to a temperature measuredwithin the dense phase bed.
 16. The method of claim 8, wherein thequench medium is introduced both above and within a dense phase bed ofthe heat carrier.
 17. The method of claim 1, wherein the solid heatcarrier is sand.
 18. The method of claim 8, further comprising flowingat least a portion of the solid heat carrier through a heat exchanger toremove heat from the reheater.
 19. An apparatus for pyrolysis of abiomass feedstock, the apparatus comprising: (a) an upflow, entrainedbed pyrolysis reactor; (b) a cyclone having (i) an inlet incommunication with an upper section of the pyrolysis reactor, (ii) asolids-enriched fraction outlet in communication with a reheater and(iii) a solids-depleted fraction outlet in communication with apyrolysis product condensation section; and (c) a quench liquiddistribution and control system in communication with the reheater. 20.A reheater for combusting solid char, separated from a pyrolysiseffluent, in the presence of a solid heat carrier that is recycled to apyrolysis reactor, the reheater comprising one or more points of quenchmedium introduction along its axial length.